The use of centrifuges is common in hematology for the preparation and spinning of plasma and serum blood samples. Centrifugation causes the incrementally more dense red blood cells to separate out from the remaining plasma. This is useful for determining the packed cell volume hematocrit value of whole blood, as well as for determining other hematological parameters.
A typical centrifuge of the type to which the present invention relates, is a hematocrit centrifuge such as disclosed in U.S. Pat. No. 4,738,655, and sold commercially under the brand name HemataSTAT.TM. by Separation Technology, Altamonte Springs, Fla. HemataSTAT.TM. models C-70 and C-70B, for example, comprise steep angle rotor heads providing reduced sample preparation spin times and including built-in, digital hematocrit reading capabilities. Though the invention is particularly applicable to such devices which are designed to determine hematocrit values using capillary tube samples, the invention has broader application to larger tube centrifuges, as well.
To determine the hematocrit value using a microcentrifuge, like the HemataSTAT.TM. centrifuge, a sample of blood is first drawn into a capillary tube (typically a 75 mm heparinized capillary tube of either 0.5 mm or 1.1 mm inside diameter) using a lancet. One end of the tube is sealed, such as with a clay plug, after drawing the sample. The filled and sealed tube is then inserted, clay end down, into one of a plurality of tube holders located in inwardly and upwardly directed channels, angularly-spaced about the centrifuge head. After spinning the sample, the tube is removed from the holder and placed in a horizontal groove located at a reader station on the front of the centrifuge. Blood component interface data entries are made (viz. positions of clay/red cell, red cell/plasma and plasma/air interfaces marked) with the aid of a sliding pointer and data entry buttons. Relative volume calculations are then performed by a microprocessor, using identified pointer positions and known tube diameter, resulting in the display of hematocrit and estimated hemoglobin on an associated LCD display.
Existing tube holders are narrow stainless steel tubes, closed at one end and flared out to form a lip at the other. They are slid, closed end first, snugly into the rotor head channels, until the flared ends are flush with the top of the head. Though the open ends are flared, the expansion is only slight and cannot readily be gripped by the fingers for removal. Instead, conventional practice is to insert a pipe cleaner into the open end to retrieve the holder out of the channel. Because of the narrowness of the holders, tube insertion must be done carefully to avoid breakage. Also, conventional tube holders are cylindrical members with circular flared ends. So care must be taken in handling the holders that they don't roll off the table onto the floor. Moreover, holder clean-out is inhibited and bleach must be heavily diluted to avoid damage to the soldered joints.
There is increasing concern among persons working with blood samples that they will become infected with biological contaminants active in the blood. It is, therefore, a desirable objective to minimize the risk of biological hazard associated with tube breakage, blood spillage and airborne contaminants that may occur during the blood tube centrifugation spin cycle.
Conventional microcentrifuges have small insertion ports that look down on the head and provide only very limited fields of view. The center of the lid is transparent to enable a user to verify cessation of rotation before opening the lid. It is difficult to use such ports for visual inspection of the spin cavity interior to check for evidence of tube breakage and sealant plug blowout or leakage. Also, because the tube holders are opaque, external visual inspection of the condition of the tubes or build-up of clay or other debris within the holders is not possible.